1. Field of the Invention
The present invention relates to the field of dissolution testing and, in particular, to apparatuses for dissolution testing of pharmaceuticals in solid, semi-solid, or transdermal dosage form.
2. Description of the Related Art
Dissolution testing and apparatuses for performing such are known in the art. U.S. Pat. No. 4,279,860 (Smolen) and U.S. Pat. No. 4,335,438 (Smolen) provide descriptions of the art of dissolution testing. In general, dissolution testing is used to determine the rate of dissolution of a material in a solution. For example, dissolution testing may be used to determine the rate of dissolution of pharmaceuticals in dosage form in specific test solutions to simulate digestion in a human. The requirements for such dissolution testing apparatuses are provided in United States Pharmacopeia (USP), Edition XXII, Section 711, Dissolution (1990).
Conventional dissolution testing apparatuses have one or more test vessels in which test solutions may be placed. One conventional configuration of a dissolution testing apparatus has, for each test vessel, a basket-type stirring element consisting of a metal shaft with a cylindrical basket at the end. After placing the dosage to be dissolved into the basket, the stirring element is lowered into the test solution near the center of the vessel and rotated at a specified rate (typically measured in revolutions per minute (RPM)) for a specified duration. Samples of the test solutions may be periodically withdrawn from the vessels to determine the degree of dissolution of the dosages as a function of time.
Another conventional configuration of a dissolution testing apparatus has a paddle-type stirring element consisting of a metal shaft with a metal blade at the end. In dissolution testing with this type of apparatus, the stirring element is rotated within the test solution with the dosage at the bottom of the vessel.
In either conventional configuration, the temperature of the test solutions is maintained at the required level (e.g., 37 degrees centigrade) by placing the test vessels in a water bath. The temperature of the water bath is typically controlled by an external water pump/heater which continually recycles water between the water bath and the pump/heater. The temperature of a test solution within one of the test vessels may be measured directly by inserting a thermometer into the test solution or indirectly by measuring the temperature of the water bath, either in the water bath itself or within the water pump/heater. Direct temperature measurement of the test solutions is not permitted during the actual dissolution testing procedure. As a result, only indirect temperature measurements are available during the testing procedure.
Conventional dissolution testing apparatuses have a number of problems. As just discussed, conventional apparatuses do not support direct measurement of test solution temperatures during testing procedures. Moreover, since all test vessels of a dissolution testing apparatus are placed within the same water bath, the temperatures for all test solutions for a specific testing procedure are the same. In addition, water baths have problems related to leaking, evaporation, and algae growth. As a result, water baths must be emptied, cleaned, and refilled periodically. Furthermore, the time required to heat test solutions using conventional water bath dissolution testing apparatuses is long--typically 30 to 45 minutes.
What is needed is an improved dissolution testing apparatus that eliminates or reduces the problems associated with conventional apparatuses.
It is accordingly an object of this invention to overcome the disadvantages and drawbacks of the known art and to provide improved apparatuses for dissolution testing.
It is a further object of this invention to provide a dissolution testing apparatus that does not rely upon a water bath to control the temperature of the test solutions in one or more test vessels.
It is another object of this invention to provide a dissolution testing apparatus that provides for direct measurement of test solution temperature during actual dissolution testing procedures and still conform to the USP dissolution test requirements.
It is yet another object of this invention to provide a dissolution testing apparatus that reduces the time required to heat the test solutions to the desired levels for dissolution testing.
Further objects and advantages of this invention will become apparent from the detailed description of a preferred embodiment which follows.